clCreateSubBuffer

Creates a buffer object (referred to as a sub-buffer object) from an existing buffer object.

cl_mem clCreateSubBuffer ( cl_mem buffer,
  cl_mem_flags flags,
  cl_buffer_create_type buffer_create_type,
  const void *buffer_create_info,
  cl_int *errcode_ret)

Parameters

buffer

A valid object. Cannot be a sub-buffer object.

flags

A bit-field that is used to specify allocation and usage information about the image memory object being created. The following table describes the possible values for flags:

cl_mem_flags Description
CL_MEM_READ_WRITE This flag specifies that the memory object will be read and written by a kernel. This is the default.
CL_MEM_WRITE_ONLY

This flags specifies that the memory object will be written but not read by a kernel.

Reading from a buffer or image object created with CL_MEM_WRITE_ONLY inside a kernel is undefined.
CL_MEM_READ_ONLY

This flag specifies that the memory object is a read-only memory object when used inside a kernel.

Writing to a buffer or image object created with CL_MEM_READ_ONLY inside a kernel is undefined.
CL_MEM_USE_HOST_PTR

This flag is valid only if host_ptr is not NULL. If specified, it indicates that the application wants the OpenCL implementation to use memory referenced by host_ptr as the storage bits for the memory object.

OpenCL implementations are allowed to cache the buffer contents pointed to by host_ptr in device memory. This cached copy can be used when kernels are executed on a device.

The result of OpenCL commands that operate on multiple buffer objects created with the same host_ptr or overlapping host regions is considered to be undefined.
CL_MEM_ALLOC_HOST_PTR

This flag specifies that the application wants the OpenCL implementation to allocate memory from host accessible memory.

CL_MEM_ALLOC_HOST_PTR and CL_MEM_USE_HOST_PTR are mutually exclusive.
CL_MEM_COPY_HOST_PTR

This flag is valid only if host_ptr is not NULL. If specified, it indicates that the application wants the OpenCL implementation to allocate memory for the memory object and copy the data from memory referenced by host_ptr.

CL_MEM_COPY_HOST_PTR and CL_MEM_USE_HOST_PTR are mutually exclusive.

CL_MEM_COPY_HOST_PTR can be used with CL_MEM_ALLOC_HOST_PTR to initialize the contents of the cl_mem object allocated using host-accessible (e.g. PCIe) memory.

buffer_create_type and buffer_create_info

The type of buffer object to be created. The supported value for buffer_create_type is CL_BUFFER_CREATE_TYPE_REGION, which create a buffer object that represents a specific region in buffer. buffer_create_info is a pointer to the following structure:


typedef struct _cl_buffer_region {
    size_t origin;
    size_t size;
} cl_buffer_region;

(origin, size) defines the offset and size in bytes in buffer.

If buffer is created with CL_MEM_USE_HOST_PTR, the host_ptr associated with the buffer object returned is host_ptr + origin.

The buffer object returned references the data store allocated for buffer and points to a specific region given by (origin, size) in this data store.

CL_INVALID_VALUE is returned in errcode_ret if the region specified by (origin, size) is out of bounds in buffer.

CL_MISALIGNED_SUB_BUFFER_OFFSET is returned in errcode_ret if there are no devices in context associated with buffer for which the origin value is aligned to the CL_DEVICE_MEM_BASE_ADDR_ALIGN value.

errcode_ret

Returns an appropriate error code. If errcode_ret is NULL, no error code is returned.

Notes

The implementation may return the same cl_mem object with the reference count incremented appropriately for multiple calls to clCreateSubBuffer that use the same values for buffer, flags, buffer_create_type and buffer_create_info points to the same descriptor or descriptors that describe values that are exactly the same.

The result of OpenCL commands that read from and write to multiple sub-buffer objects created using clCreateSubBuffer with the same buffer object but represent overlapping regions in the buffer object is undefined. The result of OpenCL commands that read from and write to a buffer object and its sub-buffer object(s) created using clCreateSubBuffer with the same buffer object is undefined. OpenCL commands that only read from multiple sub-buffer objects created using clCreateSubBuffer with the same buffer object but represent overlapping regions in the buffer object or read from a buffer object and its sub-buffer objects should work as defined.

Errors

Returns a valid non-zero buffer object and errcode_ret is set to CL_SUCCESS if the buffer object is created successfully. Otherwise, it returns one of the following error in errcode_ret:

  • CL_INVALID_MEM_OBJECT if buffer is not a valid buffer object or is a sub-buffer object.
  • CL_INVALID_VALUE if values specified in flags are not valid; or if value specified in buffer_create_type is not valid; or if value(s) specified in buffer_create_info (for a given buffer_create_type) is not valid or if buffer_create_info is NULL.
  • CL_OUT_OF_RESOURCES if there is a failure to allocate resources required by the OpenCL implementation on the device.
  • CL_OUT_OF_HOST_MEMORY if there is a failure to allocate resources required by the OpenCL implementation on the host.

Specification

OpenCL Specification

Also see

clCreateBuffer, clEnqueueReadBuffer, clEnqueueWriteBuffer, clEnqueueCopyBuffer

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